(CNN)Dead and injured birds covered in tinsel and other decorations have been turning up in New Zealand, and animal rights campaigners are worried.
The Royal New Zealand Society for the Prevention of Cruelty to Animals (SPCA) said it received up to 30 calls in recent weeks reporting sightings of sparrows and pigeons with tinsel intentionally tied to their bodies.
"Many try to pry the foreign objects off their bodies with their beaks and feet, becoming further entangled and preventing them from eating, drinking and flying. With others, the decorations are wrapped so tightly it completely cuts off their blood circulation," SPCA spokeswoman Jessie Gilchrist told CNN.
"Those that do survive and arrive at our center are often in a very bad state, they are so malnourished and distressed that we have had to humanely euthanize them."
Since 2015, the charity said there has been over thirty cases of "decorated" birds found dead or with injuries severe enough to require euthanasia.
On Tuesday, SPCA officers were called to a house in Kilbirnie, a suburb of the capital Wellington, where they rescued several birds covered in decorations and paint. The birds were in a distressed but otherwise healthy condition.
"One pigeon had quite bright red Christmas tinsel wrapped around its wings and then the top of its head had been painted with red paint as well as its wings had been tipped with red paint," Gilchrist said.
While charges have yet to be laid against the owners of the house, Gilchrist said the case "remains an ongoing investigation."
Sparrows and pigeons -- which forage for food on the ground, in shrubs or shallow water -- face a number of threats from predators, including foxes and racoons, as well as larger birds and snakes.
But humans are perhaps the biggest threat to the birds. In 2015, New Zealand recognized all animals, including birds, as "sentient" under law, extending protections and making it easier for charities like the SPCA to prosecute people for animal cruelty.
One stated purpose of the law was to "remove uncertainty around the ill-treatment of wild animals by targeting acts of wilful or reckless ill-treatment."